Cancer is one of the most important causes of human death. Early diagnosis and treatment can make patients live longer. Therefore, there is an urgent need to develop early and accurate diagnosis method for tumors. Molecular imaging technology can be used for qualitative and quantitative analyses at cellular and molecular levels, which provides a new technology for accurate diagnosis of tumors. In recent years, various nanomaterials with unique properties have been used for tumor molecular imaging. Meanwhile, aptamers are becoming an indispensable element in the design of functional nanomaterials because of their small size, high stability, and convenient modification, especially giving nanomaterials the ability to recognize specific targets. Therefore, aptamer-functionalized nanomaterials (AFNs) provide unprecedented opportunities for the field of tumor diagnosis. Here we focus on the latest development of AFNs in the molecular imaging of tumors. First, we introduce the characteristics and advantages of common aptamer-modified organic nanomaterials and inorganic nanomaterials. Then, the applications of AFNs in fluorescence imaging, computed tomography, magnetic resonance imaging, radionuclide imaging, ultrasound imaging, photoacoustic imaging, and multimode fusion imaging are discussed. Finally, we provide some perspectives on the challenges and opportunities that have arisen from this promising area.